The invention relates generally to extending the service zone of a construction time elevator to reach higher in the elevator hoistway. In connection with so-called jump-lifts, the bottom part of an elevator hoistway is taken into use already before the building has been completed. In this case the top part of the elevator hoistway can be constructed at the same time as an elevator moving in the bottom part of the elevator hoistway already serves people on the lower floors of the building. Generally in jump-lifts the elevator car moving in the lower parts of the elevator hoistway is supported by a movable supporting platform positioned above the car in the hoistway. Often the car is moved during construction-time use with a hoisting machine supported on this supporting platform, but alternative locations for the hoisting machine also exist. The installation work in the parts of the elevator hoistway above this supporting platform is performed from a movable platform or corresponding in the elevator hoistway, which installation work comprises, among other things, the installation of guide rails and electrification in the elevator hoistway. When the elevator hoistway under construction above the supporting platform has reached a sufficient stage of completion, the completed part of the elevator hoistway can be taken into use. In this case a jump-lift is performed, where the supporting platform is raised and mounted to a higher position in the elevator hoistway. It is preferable to have a roof structure above the supporting platform, which is separate from the movable support, which roof structure forms a protective cover against weather and falling objects. The roof structure has formed the uppermost structure in the elevator hoistway beneath which all the work in the hoistway has been done. The roof structure has been positioned high above the supporting platform so as to enable working between the supporting platform and the roof structure. When the building under construction has reached a certain height or construction otherwise has reached a certain point a new roof structure has been built above the earlier and the earlier roof structure has been dismantled. The disadvantage of this procedure has been that it necessitates simultaneous presence of several roof structures. Alternatively, it is possible to lift structures of the roof structure with a worksite crane used in the construction of the building and rebuild it in a higher position. One problem with this type of arrangement is that the worksite crane is not always available when needed. When the elevator hoistway has reached its final height, a machine room has conventionally been built at the end of the elevator hoistway and after that the final machinery of the elevator has been brought there. Taking into account the above presented, a need for an improved solution for positioning the roof structure has come up.